首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   853篇
  免费   38篇
  国内免费   9篇
耳鼻咽喉   36篇
儿科学   31篇
妇产科学   46篇
基础医学   50篇
口腔科学   31篇
临床医学   62篇
内科学   133篇
皮肤病学   14篇
神经病学   53篇
特种医学   47篇
外科学   119篇
综合类   14篇
一般理论   2篇
预防医学   16篇
眼科学   144篇
药学   50篇
中国医学   8篇
肿瘤学   44篇
  2023年   6篇
  2022年   15篇
  2021年   18篇
  2020年   14篇
  2019年   29篇
  2018年   23篇
  2017年   20篇
  2016年   42篇
  2015年   35篇
  2014年   40篇
  2013年   53篇
  2012年   51篇
  2011年   55篇
  2010年   34篇
  2009年   16篇
  2008年   49篇
  2007年   59篇
  2006年   45篇
  2005年   54篇
  2004年   41篇
  2003年   44篇
  2002年   46篇
  2001年   33篇
  2000年   22篇
  1999年   19篇
  1998年   5篇
  1997年   5篇
  1996年   4篇
  1995年   4篇
  1994年   2篇
  1992年   2篇
  1991年   4篇
  1990年   3篇
  1989年   3篇
  1986年   3篇
  1985年   1篇
  1983年   1篇
排序方式: 共有900条查询结果,搜索用时 15 毫秒
101.
Hepatocyte growth factor (HGF) is a mitogen and insulinotropic agent for the β-cell. However, whether HGF/c-Met has a role in maternal β-cell adaptation during pregnancy is unknown. To address this issue, we characterized glucose and β-cell homeostasis in pregnant mice lacking c-Met in the pancreas (PancMet KO mice). Circulating HGF and islet c-Met and HGF expression were increased in pregnant mice. Importantly, PancMet KO mice displayed decreased β-cell replication and increased β-cell apoptosis at gestational day (GD)15. The decreased β-cell replication was associated with reductions in islet prolactin receptor levels, STAT5 nuclear localization and forkhead box M1 mRNA, and upregulation of p27. Furthermore, PancMet KO mouse β-cells were more sensitive to dexamethasone-induced cytotoxicity, whereas HGF protected human β-cells against dexamethasone in vitro. These detrimental alterations in β-cell proliferation and death led to incomplete maternal β-cell mass expansion in PancMet KO mice at GD19 and early postpartum periods. The decreased β-cell mass was accompanied by increased blood glucose, decreased plasma insulin, and impaired glucose tolerance. PancMet KO mouse islets failed to upregulate GLUT2 and pancreatic duodenal homeobox-1 mRNA, insulin content, and glucose-stimulated insulin secretion during gestation. These studies indicate that HGF/c-Met signaling is essential for maternal β-cell adaptation during pregnancy and that its absence/attenuation leads to gestational diabetes mellitus.  相似文献   
102.
103.
104.
PURPOSE: To review the clinical features and management of circumscribed choroidal hemangioma and determine factors predictive of poor visual outcome. DESIGN: Retrospective consecutive noncomparative interventional case series. PARTICIPANTS: Two hundred consecutive patients with circumscribed choroidal hemangioma. MAIN OUTCOME MEASURES: The main outcome measures were analyzed in 155 patients with follow-up of at least 3 months and included complete resolution of subretinal fluid, worsening of visual acuity (more than 2 Snellen lines), and poor final visual acuity (20/200 or worse). RESULTS: The patients were seen at a mean age of 45 years with symptoms of decreased visual acuity (81%), visual field defect (7%), metamorphopsia (3%), floaters (2%), progressive hypermetropia (1%), photopsia (1%), pain (1%), and no symptoms (6%). The referring diagnoses were choroidal hemangioma (29%), choroidal melanoma (29%), choroidal metastasis (9%), retinal detachment (6%), central serous chorioretinopathy (5%), and others. The tumor had a median base of 6.0 mm and median thickness of 3.0 mm. Secondary retinal detachment in the foveal region was present in 81% of the patients. Initial treatment included observation (51%), laser photocoagulation (44%), plaque radiotherapy (4%), external beam radiotherapy (1%), surgical repair of retinal detachment (1%), and enucleation for painful neovascular glaucoma (1%). Kaplan-Meier estimates revealed complete resolution of subretinal fluid in 60% patients at 5 years and 76% patients at 10 years follow-up. By multivariable analysis, clinical factors predictive of complete resolution of subretinal fluid included shorter duration of symptoms (P = 0.03) and inferior quadrant location of tumor (P = 0.001). At initial presentation, 82 of 155 (53%) patients had poor visual acuity (20/200 or worse), and 73 of 155 (47%) patients had good to moderate visual acuity (20/100 or better). Of those 82 patients with poor initial vision, poor final vision was found in 54% at 5 years and 80% at 10 years. Of the 73 patients with good to moderate initial vision, poor final vision was found in 12% at 5 years and 43% at 10 years. By multivariable analysis, clinical factors predictive of poor final visual acuity included poor initial visual acuity (P < 0.001), failure of previous laser photocoagulation before referral (P = 0.01), and tumor management with observation after referral (P = 0.02). Worsening of visual acuity (by more than 2 Snellen lines) was observed in 8% at 5 years and 28% at 10 years of those 82 patients who were initially seen with poor vision. Worsening of visual acuity was found in 10% at 5 years and 30% at 10 years of those 73 patients who initially were seen with good to moderate vision. CONCLUSIONS: Circumscribed choroidal hemangioma is a rare intraocular tumor. In 38% of cases, this tumor is initially misinterpreted before referral as choroidal melanoma or metastasis. Visual acuity is poor in more than 60% of patients at 10 years, despite successful control of associated subretinal fluid in 76% patients.  相似文献   
105.
BackgroundCoronavirus disease 2019 (covid-19), which causes a pandemic in the world, has started to appear in turkey since march 2020. Healthcare workers are at the top of the groups most at risk for covid-19 infection, which can have a negative impact on psychological state.ObjectivesIt was aimed to evaluate anxiety and depression levels among healthcare workers.Methodsthis cross-sectional study performed via an online survey in april 2020. Participants answered questions about sociodemographic features, personal views and experiences about covid-19 and the hospital anxiety and depression scale (hads).ResultsA total of 300 healthcare workers,193 men and 107 women, participated in the survey. According to hads, 44.6% of participants scored above anxiety and 68.2% scored above depression cut-off points. Being younger than 50 and taking care of covid-19 patients in hospitals were independently associated with anxiety risk. Female gender, young age (less than 50) and having comorbidity were independent risk factors for depression.ConclusionHealthcare workers were at high risk of anxiety and depression during covid-19 outbreak. For this reason, psychological support should be given, especially to the group with high risk.  相似文献   
106.
PURPOSE: To determine secretory IgA epitopes in tears of extended-wear soft contact lens wearers and non-wearing controls. METHODS: We developed enzyme-linked immunosorbent assays (ELISA) to determine the tear concentrations of two epitopes of secretory IgA, the IgA alpha-chain and the secretory component. These epitopes were measured in basal tears of 20 individuals in 6 nights of extended wear of etafilcon A soft contact lenses and in 19 non-lens-wearing individuals. RESULTS: Levels of IgA alpha-chain immunoreactivity were significantly decreased in the lens-wearing group compared to non-lens wearers. However, the level of secretory component immunoreactivity was not significantly different between groups. IgA alpha-chain and secretory component immunoreactvity were highly correlated; however, some samples showed a marked variation between these two values. CONCLUSION: Tear concentrations of sIgA epitopes are significantly reduced in extended-wear contact lens wearers, and may contribute to the increased susceptibility to ocular infection seen in this group.  相似文献   
107.
The essential oil composition and antimicrobial activity of Osmitopsis asteriscoides, a medicinal plant used in traditional herbal preparations in South Africa has been investigated. Three different antimicrobial methods (disc diffusion, minimum inhibitory concentration by micro-titer plate and time-kill studies) were comparatively evaluated against Candida albicans, Staphylococcus aureus and Pseudomonas aeruginosa. A preliminary screening was done using the disc diffusion method on nine bacterial and four fungal isolates. Minimum inhibitory concentrations showed some correlation with the disc diffusion method. However, time-kill studies appear to be a more superior method for determining antimicrobial activity of volatile compounds such as essential oils. Two moderately susceptible and one resistant organism were selected to further demonstrate the variability between the three methods. The antimicrobial activity of the essential oil, tested by means of time-kill methodology at concentrations ranging from 0.5 to 2% (v/v) indicate a strong fungicidal activity against Candida albicans and the oil was also found to be bacteriostatic against Staphylococcus aureus in a concentration-dependent manner. The essential oil rapidly reduced viable counts of Pseudomonas aeruginosa, but regrowth was noted after 240 min. The results have been generated in duplicate in separate microbiology laboratories using different time-kill methods and the results are congruent. The two major essential oil components camphor and 1,8-cineole were investigated indicating the positive antimicrobial efficacy of 1,8-cineole independently and in combination with camphor. In addition to (-)-camphor and 1,8-cineole, 40 compounds were identified by GC-MS in the hydro-distilled essential oil. The high concentration of cineole and camphor and their synergistic effect is presented as a possible explanation for the traditional use of Osmitopsis asteriscoides for treating microbe-related illnesses.  相似文献   
108.
Kinesthesia may be defective in patients with Parkinson's disease (PD), and this defect conceivably has a role in parkinsonian hypokinetic symptoms. In the present study, PD patients used kinesthetic perception to estimate the amplitude of passive angular displacements of the index finger about the metacarpophalangeal joint and to scale them as a percentage of a reference stimulus. The reference stimulus was either a standard kinesthetic stimulus preceding each test stimulus (task K) or a visual representation of the standard kinesthetic stimulus (task V). In task V, the PD patients' underestimation of the amplitudes of finger perturbations was significantly greater than that of normal subjects, but not for task K. PD patients' underestimation was also greater in task V than in task K; the difference between the underestimations was significantly greater than for normal subjects. These results suggest that, when kinesthesia is used to match a visual target, distances are perceived to be shorter by the PD patients. Assuming that visual perception is normal, kinesthesia is “reduced” in PD patients. This reduced kinesthesia, when combined with the well-known reduced motor output and probably reduced corollary discharges, implies that the sensorimotor apparatus is “set” smaller in PD patients than in normal subjects.  相似文献   
109.
This study was carried out to investigate comparatively the frequency of apoptosis in lung epithelial cells after intratracheal instillation of endotoxin [lipopolysaccharide (LPS)] in rats and the role of tumor necrosis factor alpha (TNF-alpha) on apoptosis, and the effects of erdosteine and N-acetylcysteine on the regulation of apoptosis. Female Wistar rats were given oral erdosteine (10-500 mg kg(-1)) or N-acetylcysteine (10-500 mg kg(-1)) once a day for 3 consecutive days. Then the rats were intratracheally instilled with LPS (5 mg kg(-1)) to induce acute lung injury. The rats were killed at 24 h after LPS administration. Lung tissue samples were stained with hematoxylin-eosin for histopathological assessments. The apoptosis level in the lung bronchial and bronchiolar epithelium was determined using the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick endlabelling) method. Cytoplasmic TNF-alpha was evaluated by immunohistochemistry. Pretreatment with erdosteine and pretreatment with N-acetylcysteine at a dose of 10 mg kg(-1) had no protective effect on LPS-induced lung injury. When the doses of drugs increased, the severity of the lung damage caused by LPS decreased. It was found that as the pretreatment dose of erdosteine was increased, the rate of apoptosis induced by LPS in lung epithelial cells decreased and this decrease was statistically significant in doses of 300 mg kg(-1) and 500 mg kg(-1). Pretreatment with N-acetylcysteine up to a dose of 500 mg kg(-1) did not show any significant effect on apoptosis regulation. It was noticed that both antioxidants had no significant effect on the local production level of TNF-alpha. These findings suggest that erdosteine could be a possible therapeutic agent for acute lethal lung injury and its mortality.  相似文献   
110.
In this study we aimed to determine the role of piracetam (PIR) in preventing radiation induced cochlear damage after total-cranium irradiation (radiotherapy; RT). Male albino guinea pigs used in the study were randomly divided into three groups. Group 1 (Control group) (n=11) received neither PIR nor irradiation, but received saline solution intraperitoneally (i.p.) and received sham irradiation. Group 2 (RT group) (n=32) was exposed to total cranium irradiation of 33 Gy in 5 fractions of 6.6 Gy/d for five successive days, with a calculated (alpha/beta=3.5) biological effective dose of fractionated irradiation equal to 60 Gy conventional fractionation, then received saline solution for five successive days i.p. Group 3 (PIR+RT group) (n=33) received total cranium irradiation, plus 350 mg/kg per day PIR for five successive days i.p. After the last dose of RT, the guinea pigs were all sacrificed at the 4th, 24th and 96th hours, respectively. Their cochleas were enucleated for histopathologic examination. It was observed that total cranium irradiation (RT group) promoted degeneration in stria vascularis (SV), spiral ganglion cells (SG), outer hair cells (OHC) and inner hair cell (IHC) of cochleas at these times (p<0.05). While in the PIR+RT group, there was no statistically significant difference on radiation-induced cochlear degeneration in SV and OHC at 4th (p>0.05) and IHC at 4th, 24th hours (p>0.05), there was a significant difference on radiation-induced cochlear degeneration in SV and OHC at 24th and 96th hours (p<0.05), IHC at 96th hour (p<0.05) and SG at 4th, 24th and 96th hours (p<0.05). There was no any cochlear degeneration in the control group. Piracetam might reduce radiation-induced cochlear damage in the guinea pig. These results are pioneer to studies that will be performed with PIR for radiation toxicity protection.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号